Wireless local area network (wlan) as a public land mobile network for wlan/telecommunications system interworking

ABSTRACT

A telecommunications system includes a Public Land Mobile Network for providing wireless service to users and a wireless local area network functioning outside the said PLMN as a separate PLMN. An inter-PLMN backbone interfaces the WLAN to the PLMN, and an interworking function is coupled to the WLAN to provide seamless interactions between the PLMN and the WLAN to increase available service bandwidth provided for users of the PLMN.

FIELD OF THE INVENTION

The present invention generally relates to network communications and,more particularly, to a method and system for interworking wirelesslocal area networks (WLAN) as a public land mobile network (PLMN) forWLAN-UMTS (universal mobile telecommunications system) communications.

BACKGROUND OF THE INVENTION

Universal Mobile Telecommunications System (UMTS) is a ‘thirdgeneration’ (3G) mobile communications system developed within aframework known as IMT-2000 (International MobileTelecommunications-2000). UMTS will play a key role in creating the massmarket for high-quality wireless multimedia communications. UMTS willenable many wireless capabilities, delivering high-value broadbandinformation, commerce and entertainment services to mobile users viafixed, wireless and satellite networks. UMTS will speed convergencebetween telecommunications, information technology, media and contentindustries to deliver new services and create revenue-generatingservices. In most instances, UMTS will deliver low-cost, high-capacitymobile communications with data rates up to the order of 2 Mbit/secunder stationary conditions with global roaming and other advancedcapabilities.

One drawback of the UMTS network is high cost of spectrum and low datarates as compared to WLANs (Wireless Local Area Networks). It is thusadvantageous to complement UMTS with unlicensed band, high data rateWLANs such as IEEE 802.11 and ETSI Hiperlan2 to save UMTS radioresources and increase the efficiency of the UMTS RAN (Radio AccessNetwork).

Therefore, a need exists for a system and method, which utilizes WLANbandwidth to supplement UMTS bandwidth to increase overall performanceand efficiency. A further need exists for an architecture where the WLANcoverage area interacts with a UMTS network as another Public LandMobile Network (PLMN) through an inter-PLMN backbone.

SUMMARY OF THE INVENTION

A telecommunications system in accordance with the present inventionincludes a Public Land Mobile Network (PLMN) for providing wirelessservice to users, and a wireless local area network (WLAN) functioningoutside the PLMN. An inter-PLMN backbone interfaces the WLAN to thePLMN, and an interworking function is coupled to the WLAN to provideseamless interactions between the PLMN and the WLAN to increaseavailable service bandwidth provided for users of the PLMN.

In other embodiments, the PLMN may include SM/GMM (session management(SM)/GPRS mobility management (GMM)) procedures which are reused in theWLAN due to the use of an adaptation layer in a mobile dual-protocolstack and in the Interworking Function (IWF) to WLAN interface to mimicthe functionality of an RRC (Radio Resource Control). The system mayfurther include a GPRS tunneling protocol (GTP) tunnel between a GGSNand the IWF which is used only for downlink traffic coming from the GGSNto reduce system traffic. The system may include a single point ofattachment to a service provider to serve the PLMN and attached WLANs toretain control over a customer base in the WLAN.

A method for increasing bandwidth of a Public Land Mobile Network(PLMN), includes connecting a wireless local area network (WLAN) to thePLMN through an inter-PLMN interface, and providing an interworkingfunction, which communicates with the interface to convert protocolsbetween the PLMN and the WLAN such that communications received from theWLAN appear to be from another UMTS/GPRS PLMN and communications sent tothe WLAN appear to be from within the WLAN.

A method for employing a wireless local area network (WLAN) as a publicland mobile network (PLMN) includes connecting a Universal MobileTelecommunications System (UMTS) PLMN to a WLAN through an inter-PLMNbackbone using a Gp interface providing interfaces toward the UMTS PLMNand the WLAN by employing an interworking function which providesprotocol compatibility, and servicing users of the UMTS PLMN using theWLAN.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages, nature, and various additional features of the inventionwill appear more fully upon consideration of the illustrativeembodiments now to be described in detail in connection withaccompanying drawings wherein:

FIG. 1 is a schematic diagram of a system architecture having a WLANinterfaced to a UMTS PLMN in accordance with one embodiment of thepresent invention;

FIG. 2 is an exemplary system diagram showing a WLAN interfaced to aUMTS PLMN, to be employed as a WLAN PLMN, in accordance with the presentinvention;

FIG. 3 is a user plane stack diagram showing an interworking functioninterface, which creates protocol compatibility between a WLAN mobilestation and a UMTS PLMN in accordance with one embodiment of the presentinvention;

FIG. 4 is a control plane stack diagram showing an interworking functioninterface which creates protocol compatibility between a WLAN mobilestation and a UMTS PLMN in accordance with one embodiment of the presentinvention; and

FIG. 5 is an illustrative diagram showing a routing area change betweena WLAN and a UMTS PLMN in accordance with one embodiment of the presentinvention.

It should be understood that the drawings are for purposes ofillustrating the concepts of the invention and are not necessarily theonly possible configuration for illustrating the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a method and system for utilizingavailable bandwidth in wireless/radio networks. An architecture isprovided where the Wireless Local Area Network (WLAN) coverage areainteracts with a Universal Mobile Telecommunications system (UMTS)network as another Public Land Mobile Network (PLMN) through aninter-PLMN backbone.

Roaming is employed between two PLMNs. A possible way to supportinter-PLMN roaming is discussed very briefly in 3G TS 23.003 under theheading “Numbering, addressing and identification”. When a mobilestation (MS), or user equipment (UE), roams from an SGSN (Serving GPRSSupport Nodes) to an SGSN in another PLMN, the new SGSN may not haveaccess to the address of the old SGSN. Instead, the SGSN transforms theold RA (radio access) information to a logical name. The SGSN may thenacquire the IP address of the old SGSN from a domain name server (DNS),using the logical address (e.g., a logical SGSN). Every PLMN shouldinclude one DNS server.

Introducing the DNS concept in GPRS provides the possibility of usinglogical names instead of IP addresses when referring to, e.g., GPRSSupport Nodes (GSNs), thus providing flexibility in addressing of PLMNnodes. Another way to support seamless inter-PLMN roaming is to storethe SGSN IP addresses in HLR (home location register) and request theaddresses when needed. TS 23003 states that a Public Land Mobile Network(PLMN) is uniquely identified by its PLMN identifier.

PLMN-Id is made of Mobile Country Code (MCC) and Mobile Network Code(MNC). According to the specifications, there can be places where MSscan receive two cells in different PLMNs, and there can existoverlapping PLMNs too. In such a case, the NAS (Non Access Stratum) maycontrol the cell selection by maintaining lists of equivalent PLMNs andforbidden PLMNs. An Equivalent PLMN is a PLMN considered as equivalentto the selected PLMN by the UE for PLMN selection, cell selection, cellreselection and handover according to the information provided by theNAS. In the case, that the mobile has a stored “Equivalent PLMNs” listthe mobile shall only select a PLMN if it is of a higher priority as thecurrent serving PLMN, which are stored in the “Equivalent PLMNs” list.This list is replaced or deleted at the end of each location updateprocedure, routing area update procedure and GPRS attach procedure.Similarly, the MS shall contain a list of “forbidden PLMNs for GPRSservice” where a Forbidden PLMN is a PLMN that the MS is not allowed toattach. The specification also states that as long as the new PLMN isnot in the forbidden list, the MS shall initiate the normal routing areaupdate procedure when moving from one PLMN's routing area to anotherPLMN's routing area.

A number of architectures are provided to interwork between the WLANcoverage area and other radio access technologies (RATs), such as UMTS.A novel approach is presented to assist in using any existing WLANcoverage area to complement UMTS networks by defining the WLAN asanother PLMN and then using the inter-PLMN backbone to communicatebetween the WLAN and the UMTS network. The QoS (quality of service)negotiation, mobility, and AAA (Authentication, Authorization andAccounting) procedures of the 3G network are re-used. Anyone can own aWLAN. In other words, two heterogeneous interworking networks may not beowned by the same service provider. The present invention provides ameans to support “roaming” capability from a logical-PLMN-based-WLAN tohis home PLMN. Advantageously, the present invention can work with anytwo heterogeneous network systems (e.g., General Packet Radio Service(GPRS)/CDMA 2000, a DSL network, a cable network or a satellite network)that needs to interwork with each other using the inter PLMN roamingstandards.

It is to be understood that the present invention is described in termsof an illustrative WLAN-UTMS UMTS system architecture; however, thepresent invention is much broader and may include any wireless/radionetwork system(s), which are capable of providing telecommunicationservices. It should be understood that the elements shown in the figuresmay be implemented in various forms of hardware, software orcombinations thereof. Preferably, these elements are implemented inhardware on one or more appropriately programmed general-purposedevices, which may include a processor, memory and input/outputinterfaces.

Referring now in specific detail to the drawings in which like referencenumerals identify similar or identical elements throughout the severalviews, and initially to FIG. 1, a system architecture 10 for integratingvoice, data, video and other services over wireless/radio networks isshown. System architecture 10 is presented as an exemplary WLAN-UMTSenvironment for employing the inventive method and system in accordancewith the present invention. Details of the individual block componentsmaking up the system architecture which are known to skilled artisanswill only be described in details sufficient for an understanding of thepresent invention.

The present invention is illustratively described in terms of a UMTSnetwork 12 and a WLAN wireless network 14 (e.g., IEEE 802.11 andHIPERLAN2 standards may be employed by these networks). UMTS mobilenetwork 12 (e.g., a third generation (3G) network) communicates with aradio access network (RAN) 8 which comprises a Node B 11 and RadioNetwork Controller (RNC) 9. The RAN 8 in turn is attached to a CoreNetwork (CN) 13 which comprises packet based services such as a SGSN(Serving GPRS Support Node) 28, circuit based services, such as a MSC(Mobile Switching Center) 21 and gateways to other PLMNs, such as GGSN(Gateway GPRS Support Nodes) 24. Core network 13 supportsconnections/interfaces with public switched telephone networks (PSTN) 5and the Internet 7.

Other components may be included in a core network 13. For example, ahome location register 50 may be provided which stores the subscriberprofile and authentication vectors of mobile stations (MS) 40. By thepresent invention, network 12 (e.g., a PLMN) is interfaced to a wirelessLAN 14 through a G interface, called the Gp interface, using BorderGateway (BG) 26 and the inter-PLMN backbone network 18, by employing aninterworking function 25. MS 40 connects at an access point 30, and MS40 is seamlessly switched between WLAN 14 and UMTS 12 in accordance withthe present invention when MS 40 roams between the radio accessnetworks.

WLAN interworking function (IWF) 25 bypasses the RNC 9 and connects toSGSN 28 (assuming packet switched (PS) services). The GGSN 24 takes careof the mobility at the packet data (PD) layer, but the IWF 25 will needto communicate with the SGSN 28 to provide the mobility for the handoffbetween the two physical layer interfaces of network 12 and 14. This canbe achieved by implementing the Gp interface between the IWF 25 and theSGSN 28 as shown in FIGS. 3 and 4. The 3G SGSN 28 then sees the IWF 25as a ‘logical’ GGSN or pseudo-SGSN in another PLMN.

The SGSN (IWF)-GGSN portion may become a bottleneck in handling highdata rate WLAN hotspots. In that case, another option is to use a GPRStunneling protocol (GTP) tunnel 11 between GGSN 24 and IWF 25 is usedonly for downlink traffic coming from the GGSN 24 for user equipment(UE) at MS 40. For all other traffic, the WLAN 14 provides a commonInternet access to the UE. This reduces the traffic through theSGSN-GGSN.

Referring to FIG. 2, in this example, there are two kinds of backbonenetworks. These are called lntra-PLMN backbone network 20 and Inter-PLMNbackbone network 18. The intra-PLMN backbone network 20 preferablyincludes an Internet Protocol (IP) network interconnecting GSNs (GatewaySupport Nodes) (not shown) within the same PLMN 12. The inter-PLMNbackbone network 18 preferably includes a data packet (DP) networkinterconnecting GSNs and intra-PLMN backbone networks 18 in differentPLMNs (e.g., PLMNs 12 and 14). Every intra-PLMN backbone network 18 ispreferably a private DP network intended for packet domain data andsignaling only. In accordance with the present invention, a WLANbackbone network 22 is employed as an intra-PLMN backbone.

Two intra-PLMN backbone networks 20 and 22 are advantageously connectedvia a Gp interface using a Border Gateway (BG) 26 and inter-PLMNbackbone network 18. The inter-PLMN backbone network 18 is selected by aroaming agreement between providers or other default options, which maybe programmed into the networks. The roaming agreement will alsopreferably include the BG 26 security functionality as well. Theinter-PLMN backbone 18 may be included in Packet Data Network 16, e.g.,the public Internet or a leased line, although other types of networksmay be included.

WLAN PLMN 14 includes a plurality of access points 30 which are providedto permit wireless user equipment (UE) or mobile stations (MS) to accessand use the WLAN. Such information may be transferred over Packet DataNetwork 16 by employing a router 27 and appropriate security andprotocol interfaces (e.g., Gi).

By the present invention, WLAN 14 is implemented as another PLMN and anIWF (Interworking Function) 25 interacts with the UMTS network 12through the inter-PLMN backbone 18 over the Gp interface. One approachin implementing this architecture includes treating the IWF 25 as alogical SGSN (similar to SGSNs 28), which communicates with an “old”SGSN in the UMTS PLMN over the Gp interface in a similar fashion as whenan SGSN and/or a GGSN are in different PLMNs, and they areinterconnected via the Gp interface. In this way, the UMTS PLMN 12interfaces through IWF 25 in a WLAN environment as though the IWF 25were an SGSN or GGSN in another PLMN. The Gp interface provides thefunctionality of the Gn interface, plus security functionality neededfor inter-PLMN communication. The security functionality is based onmutual agreements between operators (e.g., between operators of the WLANnetwork 14 and the 3G (UMTS) network 12). The Gn interfaces interfacebetween SSGNs and GGSNs of a same PLMN, while Gp interfaces interfacebetween SSGNs and GGSNs of different PLMNs.

Referring to FIGS. 3 and 4, a user plane stack and a control plane stackfor architecture 10 of FIG. 2 are illustratively shown. A logical SGSNor pseudo-SGSN is provided by IWF 25 to act as an interface. In thisway, a mobile station (MS) 40 associated with a WLAN may interface witha SGSN 28 associated with a 3G UMTS PLMN 12 in accordance with thepresent invention. It is to be understood that the protocol stacks maybe modified according to specific applications and roaming agreement(including security features) and the stacks shown are illustrative andfor the purpose of demonstrating a particularly useful embodiment of thepresent invention. FIG. 3 illustrates user (data) plane stack protocolwhile FIG. 4 illustrates control/signaling stack protocol.

As one skilled in the art would understand, the user plane stack of MS40 in FIG. 3 has a dual stack (WLAN and UMTS) which includes anApplications layer, a transmission control protocol/user datagramprotocol (TCP/UDP) layer, an Internet protocol layer (IP), a WLAN mediumaccess control/radio link control/logical link control (MAC/RLC/LLC)layer and the WLAN physical layer; the UMTS part also includes thepacket data convergence protocol (PDCP), radio link control (RLC) andMAC layers, and a UMTS physical layer (PHY). The IWF 25 transfers anydata/information received from the mobile over the WLAN interface to theUMTS network over an interface compatible with an SGSN of a 3G UMTSsystem. For example, the data received over WLAN MAC/LLC is transferredto the UMTS SGSN 28 by IWF 25 over a gateway tunneling protocol for theuser plane (GTP-U), UDP and an IP.

Similar conversion is performed in the control plane. As one skilled inthe art would understand, the control plane stack of MS 40 in FIG. 4includes a common Signaling Applications layer, a session managementlayer (SM), a GPRS mobility management layer (GMM); an RRC (RadioResource Control) layer, a RLC/MAC layer and the UMTS physical layer forthe UMTS interface; and over the WLAN interface: an adaptation layer forradio resource control (RRC), a WLAN MAC/LLC layer, and a WLAN PHYlayer. The adaptation layer (AL) in the MS 40 mimics the interfacefunctions that correspond to the RRC service. This is necessary to reusethe session management (SM) and GPRS mobility management (GMM) layers ofthe 3G mobile stack even in WLAN. The IWF adaptation layer (AL) mightplay the role of a light RRC and transfer any control signalinginformation (SM/GMM messages) from the MS 40 received over the WLANMAC/LLC layers to SGSN 28 over a protocol compatible with an SGSN of a3G UMTS system and vice versa. As before, IWF 25 transfers SM/MMsignaling over the Gp interface to the 3G SGSN, and may be employed asthough stack were native to the 3G network.

The present invention provides at least the following advantages. Thequality of service (QoS) negotiation, mobility, MA procedures of the 3Gnetwork are employed making the entire system more efficient from thestandpoint of increased bandwidth, quality and compatibility. Allcellular operators may share WLAN resources in hot spots where systemresources may be taxed under normal traffic conditions. By institutingappropriate roaming agreements, any operator can “own” the WLAN andestablish a trust relationship with a UMTS operator. In other words, asubscriber from any operator may have “roaming” capability from alogical-PLMN-based-WLAN to his home PLMN or other designated PLMN. Thepresent invention can work with any system (GPRS/CDMA 2000) that caninterwork with WLANs.

Advantageously, deployed WLANs, in accordance with the presentinvention, provide needed bandwidth to maintain QoS for all users. Forexample, 3G operators, instead of deploying their own WLANs in hotspots,may use existing WLANs already deployed to increase their networkcapabilities. In addition, WLAN radio resources may be used to free upradio resources of the 3G RAT that a user is moving in a WLAN coveragearea. Communication between PLMNs and WLAN of the present invention isseamless by employing an IWF to create compatible protocols andinformation exchange.

Referring to FIG. 5, a diagram showing interactions between entities ina routing area change scenario are illustratively shown in accordancewith one example embodiment of the present invention. The diagram showsa mobile station (MS) 40, a UMTS Terrestrial Radio Access Network(UTRAN) 42, a new IWF-SGSN 44 (created to employ the resources of aWLAN), an old 3G-SGSN 46, a GGSN 24, a new mobile switchingcenter/visitor location register (MSC/VLR) 48, a home location register(HLR) 50 and an old MSC/VLR 52. In this scenario, MSis moving into ahigh traffic area (hot spot) where a UMTS' resources are heavily loaded.The system employs the WLAN (IWF) to more efficiently use the resourcesof the 3G UMTS supplementing its capabilities with the WLAN. In step101, a routing area update request is made by MS 40 to the IWF-SGSN 44.If MSis in packet mobility management (PMM) idle, IWF-SGSN 44 makes acontext request over a Gp interface to old 3G SSGN 46 to perform arouting area update, in step 101. If in idle mode, IWF 44 sends an SGSNContext Request in step 102 to SGSN 46. SGSN 46 provides a contextresponse to IWF-SGSN 44 in step 105. If MS 40 is in a PMM connectedmode, an SRNS (Serving Radio Network Subsystem) context response is madeto UTRAN 42 in step 103 and a response is sent back to 3G-SGSN 46 instep 104.

When a subscriber is in a WLAN coverage area, security functions may behandled between MS 40 and IWF-SGSN 44 in step 106 in the same way as ifit were in a UMTS coverage area. Additional security procedures may beprovided in step 107 to authenticate the new IWF-SGSN 44. In step 108 acontext acknowledgement is sent from IWF-SGSN 44 to SGSN 46. In step109, IWF-SGSN 44 sends a packet data protocol context request to GGSN24, which responds with a context response in step 110.

When MS 40 roams from an SGSN 46 to an SGSN 44 in another PLMN, the newSGSN 44 may not have access to the address of the old SGSN 46. Instead,the SGSN 44 may transform the old RA information to a logical name. TheSGSN may then acquire the IP address of the old SGSN from a domain name(DNS) server, using the logical address. Every PLMN should include oneDNS server. Introducing the DNS concept in GPRS provides the possibilityof using logical names instead of IP addresses when referring to, e.g.,GSNs, thus providing flexibility in addressing of PLMN nodes. Anotherway to support seamless inter-PLMN roaming is to store the SGSN IPaddresses in HLR (home location register) 50 and request the addresseswhen needed.

Mobility

The WLAN has all the operational functions as an independent PLMN tosupport inter PLMN roaming. The WLAN can be included in the “equivalentPLMN” list of the MS at the time of attaching by the 3G network with ahigher priority so that when there is a WLAN coverage overlapping with aUMTS coverage PLMN, the WLAN PLMN is chosen by the MS. In steps 111-120,the new SGSN (IWF 25) 44 informs the HLR 50 of the change of SGSN bysending Update Location (SGSN Number, SGSN Address, and InternationalMobile Subscriber Identification (IMSI)) to the HLR 50. Requests,responses and acknowledgements are performed. Steps 111 and 114 performa Iu (interface between RNC and SGSN) release sequence when MS 40 sendsan explicit signaling connection release to UTRAN 42 upon beingvalidated by the old SGSN 46 in steps 102-105 depending on a PacketMobile Management (PMM) state of MS 40. A similar procedure is performedto update location in the visitors location register VLR between an oldVLR/MSC 52 and a new VLR/MSC 48. Steps 120-125 provide this updatesequence.

The new SGSN (IWF) 44 may not implement a Gr interface (an interfacebetween an HLR and an SGSN) with HLR 50 and so, in this case, steps111-126 and 129 may be skipped. In step 126, a location update accept issent to IWF SGSN 44 from the new VLR/MSC 48. The routing area change isupdated, accepted in step 127 and completed in step 128. In step 129,PTMSI (Packet Temporary Mobile Subscriber Identity) reallocation may beperformed and completed if needed.

The IWF is referred to as IWF 25 (FIGS. 1 and 2), and the IWF-SGSN 44 isemployed to indicate the system's interface location. These terms aresynonymous and may be readily interchanged. The method as described withreference to FIG. 5 illustratively describes the following scenario.

1. UMTS to WLAN Entry

If the UMTS SGSN covers one routing area (RA) and the WLAN coverage areais another RA, the WLAN IWF can broadcast the new routing areaidentifier (RAI) (pre-allocated by the UMTS network). By comparing theRAI stored in user equipment (UE) or mobile station (MS) in GPRS MobileManagement (GMM) context with the RAI received from the IWF, the MS orUE detects that an RA update (inter-SGSN) needs to be performed. Theprocedure is described with reference to FIG. 5. For an Inter-SGSN RAupdate, the new SGSN (IWF) informs the HLR of the change of SGSN bysending Update Location (SGSN Number, SGSN Address, and InternationalMobile Subscriber Identification (IMSI)) to the HLR. However, in thedescribed case of FIG. 5, the new SGSN (IWF) may not implement the Grinterface towards HLR and so this step along with the other identifiedsteps are skipped. The Iu release sequence happens when the UE sends anexplicit signaling connection release to a UMTS Terrestrial Radio AccessNetwork (UTRAN) upon being validated by the old SGSN depending on aPacket Mobile Management (PMM) state of the UE.

2. WLAN to UMTS Entry

Upon re-entry into the UMTS network, the UE again performs an inter-SGSNrouting area update and repeats the method of FIG. 5, except that thistime the new SGSN is the UMTS SGSN while the old SGSN is the IWF. 3Gsecurity procedures are preferably implemented to re-validate the UEwhen it goes back to the UMTS network. If in going into the WLAN, theIWF had not updated the HLR and the UMTS SGSN marked in its context aMobile Switching Center (MSC)/Visitor Location Register (VLR)association, the information in the GGSNs and the HLR is invalid, sowhen the MS initiates a routing area update procedure back to the UMTSSGSN, it triggers the MSC/VLR, the GGSNs, and the HLR information in theUMTS SGSN to be updated/validated.

Security

Advantageously, 3G security procedures may be reused to validate the UEwhen it moves to WLAN using the HLR interface with the 3G SGSN. However,additional security functionality required for inter-PLMN communicationwill be needed.

By the present invention, dual stacked mobile units and an IWF employ anadaptation layer (AL) which enables the ability to use existing SM/GMMprocedures from the mobile to the 3G SGSN for Session and Mobilitymanagement. The invention advantageously reuses the SM/GMM procedures ofUMTS even in the WLAN due to the use of an AL in the mobiledual-protocol stack and in the IWF WLAN interface to mimic thefunctionality of a light RRC. The service provider requires only onepoint of attachment to serve the 3G network as well as the attachedWLANs helping the provider retain tight control over his customer basein the WLAN as well. The present invention also has the advantage thatthe dual GTP encapsulation as in the UMTS network (GGSN-SGSN and thenSGSN-RNC) is avoided as only the GGSN-IWF encapsulation part is done inthe WLAN coverage area. No modifications to the existing UMTS networknodes are required for the interworking architecture of the presentinvention, and seamless handover is provided (e.g., no dropping of asession).

Having described preferred embodiments for wireless local area network(WLAN) as a public land mobile network for WLAN/Universal MobileTelecommunications System interworking (which are intended to beillustrative and not limiting), it is noted that modifications andvariations can be made by persons skilled in the art in light of theabove teachings. It is therefore to be understood that changes may bemade in the particular embodiments of the invention disclosed which arewithin the scope and spirit of the invention as outlined by the appendedclaims. Having thus described the invention with the details andparticularity required by the patent laws, what is claimed and desiredprotected by Letters Patent is set forth in the appended claims.

1. A wireless Local Area Network (WLAN), comprising: an access point forcommunicating with a plurality of mobile stations; and an interworkingfunction, coupled between the access point and a selected Public LandMobile Network (PLMN), via an inter-PLMN backbone, the interworkingfunction enabling communications between the selected PLMN and the WLANwherein the WLAN appears as another PLMN to the selected PLMN.
 2. TheWLAN according to claim 1, wherein the interworking function enablescommunications with the selected PLMN using the Gp interface.
 3. TheWLAN according to claim 2, wherein the interworking function performsthe functions of a logical Serving General Packet Radio Service (GPRS)Support Node (SGSN).
 4. The WLAN according to claim 3, wherein theinterworking function is viewed by the selected PLMN as an SGSN inanother UMTS/GPRS PLMN.
 5. The WLAN according to claim 1, wherein theselected PLMN includes Session Management/GPRS mobility management(SM/GMM) procedures, which are reused in the WLAN by the use of anadaptation layer in a mobile dual-protocol stack and in the IWF to WLANinterface to mimic the functionality of a Radio Resource Control (RRC)protocol sub-layer.
 6. The WLAN according to claim 1, wherein theinterworking function utilizes a GPRS tunneling protocol between a GGSNand the interworking function for downlink traffic coming from the GGSNto reduce UMTS traffic, and provides a common Internet access to allusers for all other traffic to reduce the traffic between theinterworking function and the GGSN.
 7. The WLAN according to claim 1,wherein the selected PLMN comprises a Universal MobileTelecommunications System (UMTS) network.
 8. A method for communicatingwith a selected Public Land Mobile Network (PLMN) via a wireless LocalArea Network (WLAN), comprising the steps of: connecting the WLAN to theselected PLMN through an inter-PLMN interface; and providing aninterworking function, which communicates with the interface to convertprotocols between the WLAN and the selected PLMN wherein communicationsfrom the WLAN to the selected PLMN appear to be from another PLMN, andcommunications from the selected PLMN to the WLAN appear to be fromwithin the WLAN.
 9. The method according to claim 8, wherein theproviding step comprises providing an interworking function thatcommunicates between the selected PLMN and the WLAN using the Gpinterface.
 10. The method according to claim 8, wherein the providingstep comprises providing an interworking function that mimics thefunctions of a Serving General Packet Radio Service (GPRS) Support Node(SGSN).
 11. The method according to claim 8, further comprisingutilizing a GPRS tunneling protocol between a GGSN and the interworkingfunction for downlink traffic coming from the GGSN to reduce traffic onthe selected PLMN.
 12. The method according to claim 8, furthercomprising an adaptation layer in a mobile dual-protocol stack in theinterworking to WLAN interface to mimic the functionality of a RadioResource Control (RRC) protocol sub-layer, whereby the sessionmanagement/GPRS mobility management (SM/GMM) procedures are reused inthe WLAN.
 13. A method for communicating with a mobile station and aselected Public Land Mobile Network (PLMN) in a wireless Local AreaNetwork (WLAN), comprising the steps of: broadcasting a routing areaidentifier; receiving a routing area update request from the mobilestation that enters into a coverage area of the WLAN in response to thebroadcast; transmitting the routing area update request to a SGSN of aselected PLMN, via an inter-PLMN backbone using the Gp interface,wherein the WLAN appears as a logical PLMN to the selected PLMN; andreceiving a context response from the SGSN via the inter-PLMN backbone.14. The method according to claim 13, wherein the selected PLMNcomprises a Universal Mobile Telecommunications System (UMTS) network.15. The method according to claim 13, further comprising the step ofproviding an interworking function that mimics the functions of aServing GPRS Support Node (SGSN) such that the WLAN appears as anotherPLMN to the selected PLMN.